An actively clamped bidirectional flyback converter is disclosed in the article “Experimental Analysis Of A Flyback Converter With Excellent Efficiency” as presented by U. Boeke, D. Itzenga, K. Rigbers, and R. W. De Doncker in Proceedings of Applied Power Electronic Conference (APEC) from Mar. 19 to 23, 2006, in Dallas, Tex.
This actively clamped bidirectional flyback converter is based on the reference document “Actively-Clamped Bidirectional Flyback Converter” by Gang Chen, Yim-Shu Lee, S. Y. Ron Hui, Dehong Xu, Yousheng Wang, IEEE Transactions on Industrial Electronics, volume 47, number 4, August 2000, pages 770 to 779. This converter does not include any current sensors. The on-time of the synchronous rectifier switch is taken from the pulse-width-modulator in combination with a “turn-on delay” sub-circuit.
EP 1 148 624 A1 describes an integrated circuit to drive a power M[etal-]O[xide-]S[emiconductor]F[ield]E[ffect]T[ransistor] acting as synchronous rectifier (cf. also Fabrizio Librizzi, and Pietro Scalia, “STSRx family: Mixed-signal ICs to drive synchronous rectifiers in isolated SMPSs”, STMicroelectronics, application note AN1288, July 2000).
U.S. Pat. No. 6,462,965 B1 discloses a sub-circuit to drive a power MOSFET as synchronous rectifier switch by means of one current transformer per output.
US 2003/0090914 A1 reveals a circuit including a special sub-circuit to drive a power MOSFET as synchronous rectifier by means of a second current shunt sensor.
Texas Instruments' integrated control circuit type UCC2891 and UCC2897 includes only two time delay functions to control the on-time of the two power semiconductors on the primary converter side (cf. Texas Instruments, UCC2891 Current Mode Active Clamp PWM Controller, data sheet, July 2004; Texas Instruments, UCC2897, Current Mode Active Clamp PWM Controller, data sheet, April 2005). The use of synchronous rectifier switches is only illustrated for the application of a forward converter and does not include control circuits for the timing of the synchronous rectifier switches.
The use of delayed turn on time signals to turn on both power semiconductors of a flyback converter with synchronous rectification is disclosed in the article “High efficiency flyback converter using synchronous rectification” by I. D. Jitaru, Proceedings of Applied Power Electronics Conference (APEC) from Mar. 10 to 14, 2002 in Dallas, Tex., pages 867 to 871. This converter does not use the active clamping principle. Thus, the two switches of this converter are explicitly never turned on at the same time.
U.S. Pat. No. 6,888,728 B2 includes timing circuits on the secondary side of the transformer. The timing circuits include a comparator requiring an additional supply voltage on the secondary side of the power converter. This overall effort of sub-circuits to drive the synchronous rectifier switches on the secondary side of the transformer is very high and generates significant costs. The greatest disadvantage of U.S. Pat. No. 6,888,728 B2 is the higher component effort meaning also higher cost.
JP 2005-198438 A describes a load resonant half-bridge converter with synchronous rectification. The component count of this known circuit is very high; apart from that, the load resonant converter includes a second power transformer plus a shunt resistor both generating additional power losses and thus increasing the thermal management effort. The greatest disadvantage of JP 2005-198438 A is the use of a second power transformer to monitor the input current of the load resonant circuit on the secondary side of transformer; this generates significant loss in the second power transformer.
Regarding the technological background of the present invention, reference can finally be made to U.S. Pat. No. 5,057,986 as well as U.S. Pat. No. 5,402,329.